Stratified liquefied petroleum gas—dimethyl ether compression ignition engine combustion at various intake valve open timings

Abstract

The combustion and exhaust emissions characteristics of compression ignition engine with a variable valve timing device were investigated for liquefied petroleum gas (LPG) and dimethyl ether (DME) under various LPG injection timing conditions. LPG was used as the main fuel injected directly into the combustion chamber. DME was used as an ignition promoter injected into the intake port. Different LPG injection timings were tested to verify the effects of the mixture homogeneity on the combustion and exhaust emission characteristics of the LPG and DME compression ignition engine. The average charge temperature was calculated to analyse the pollutant formation. The ringing intensity was used for the analysis of knock characteristics.

The combustion and exhaust emission characteristics differed significantly depending on the LPG injection and intake valve open timings. The carbon monoxide (CO) emission increased as the intake valve opened and LPG injection timings were retarded owing to the local mixture inhomogeneity. However, the particulate matter (PM) emission decreased and the nitrogen oxides (NO _x ) emission increased as the intake valve open timing was retarded in the diffusion combustion regime. Finally, the combustion efficiency decreased as the intake valve open and LPG injection timings were retarded.